裂缝性储层裸眼井壁失稳影响因素分析

Analysis on wellbore stability of open hole in fractrued formation

国内西部油田碳酸盐岩地层埋藏深、温度高、缝洞系统发育,生产过程中井区裸眼完井地层出现垮塌现象,堵塞、埋卡管柱。通过研究现场资料对井壁垮塌的原因进行了分析,同时,由于地层温度高、压力大,建立了考虑温度场、渗流场、裂缝产状、水化作用等因素影响的井壁垮塌预测模型,对碳酸盐岩深井高温水化地层裸眼完井垮塌机理进行了研究。研究表明,模型对维持井壁稳定的最小井底压力的预测比常规模型高2～3 MPa,提升了预测精度;随着岩石裂缝倾角的增加,其强度先减小后增加;井壁最为安全的地层是裂缝倾角为0～20°,倾向近水平最小地应力方位,其次是倾角60～90°,倾向近水平最大地应力方位;维持井壁稳定的最小井底压力随着水化后弱面内摩擦因数及弱面黏聚力的降低而增加,随着应力差的增加而增加。

Carbonate rocks in westward oilfield are characterized by deep bury, high temperature, rich in fracture-cave and well collapse, blocking and burying of testing tool always appear in the open-hole completion well formation in the process of production. The reasons of well collapse have analyzed in this article based on in-situ data, at the same time, since the high temperature and high pressure of formation, comprehensive prediction model about borehole stability has been set up, considering with temperature field, flow field, fracture occurrence and hydration. Collapse mechanism of openhole completion deep well in high temperature hydration carbon- ate stratum also been analyzed. The research results indicated that the minimum bottom hole pressure of maintain wellbore stability acquired from this model is 2-3 MPa higher than that from other conventional models, which promote prediction accuracy; rock strength increases at first and then decreases with the fracture dip from 0° to 90°; The most secure formation is that the formation dip keeps in line with direction of minimum horizontal stress and the fracture dip is lower than 20°, besides, the second is the condition that forma- tion dip consistent with maximum horizontal stress direction and fracture dip is greater than 60°. The minimum of bottom hole pressure maintaining wellbore stability increase with the decrease of inner friction coefficient and cohesive of weak surface after hydration, and increase with stress difference increasing.